定义了一个prev 一个cur 一个temp

public ListNode reverseList(ListNode head) {
    ListNode prev = null;
    ListNode cur = head;
    while (cur != null) {
        ListNode nextTemp = curr.next;
        cur.next = prev;
        prev = curr;
        cur = nextTemp;
    }
    return prev;
}

图片分析来自LeetCode
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重点就是 head.next.next=head 实际上就是把。head.next转向了。然后将head.next=null.则将head与head.next的链接翻转。
注意终止条件是head.next=null.

class Solution {
public ListNode reverseList(ListNode head) {
    if (head.next == null ) return head;
    ListNode p = reverseList(head.next);
    head.next.next = head;
    head.next = null;
    return p;
}